Power boosting in a wireless communication system

ABSTRACT

Method and apparatus for power boosting a portion of installments in transmission of a packet of data. The power boosting incorporates a power boost factor for each installment. On receipt of a negative acknowledgement after the power boosted portion of installments, transmission of the subpacket is terminated, and processing passed to a higher layer.

CLAIM OF PRIORITY

[0001] The present Application for Patent claims priority to thefollowing applications filed in the U.S. Patent & Trademark Office:

[0002] U.S. Provisional Patent Application No. 60/319,888, entitled,“Physical ARQ in a Wireless Communication System,” filed Jan. 21, 2003,

[0003] U.S. Provisional Patent Application No. 60/319,889, entitled,“Physical ARQ in a Wireless Communication System,” filed Jan. 21, 2003,and

[0004] U.S. patent application Ser. No. 10/140,087, entitled, “Methodand Apparatus for Augmenting Physical Layer ARQ in a Wireless DataCommunication System,” filed May 6, 2002.

REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT

[0005] The present Application for Patent is related to the co-pendingU.S. patent Application entitled, “Reverse Rate Indicator Detection,”having Attorney Docket No. 030168U2, filed concurrently herewith.

BACKGROUND

[0006] 1. Field

[0007] The present invention relates generally to the field of datacommunications, and more particularly, to wireless data communications.

[0008] 2. Background

[0009] In a data communication system, particularly a wireless datacommunication system, packets of data may be lost for various reasons,including poor channel conditions. The data communicated between two endusers may pass through several layers of protocols for assuring properflow of data through the system, where each layer adds certainfunctionality to the delivery of the data packet from a source user to adestination user. The proper delivery of data in at least one aspect isassured through a system of checking for error in each packet of data,and automatically requesting a retransmission of the same packet of data(ARQ mechanism), if an error is detected in the received packet of data.Independent ARQ mechanisms may be employed at different protocol layersfor flowing data between corresponding end users. The data packets aresequentially delivered from one protocol layer to another. Thesequential delivery is performed by transferring a group of data packetsat a time in a series of packets of data from one protocol layer toanother. A group of data packets may not be transferred until theprocess for retransmission of the erased packets of data in the group inthe lower protocol layer has been completed. The retransmission requestfor retransmitting an erased packet of data may be repeated severaltimes or the retransmission may take several times until the erasedpacket of data is received correctly at the destination. As a result,the retransmission process at one protocol layer may slow down the flowof data between different protocol layers in the system. In the meantime, the higher layer protocol may prematurely request forretransmission of all the packets of data in the group including thosereceived successfully at the lower layer, resulting in a veryinefficient use of communication resources when flow of data from oneprotocol layer to another is slow. As such, minimizing the lower layerpacket losses due to erasures over the air link is important as much asminimizing the delay of multiple retransmissions, in the event of apacket loss. Therefore, there is a tradeoff between the number ofretransmission attempts by a lower layer protocol layer and the delayresulting from such retransmissions that must be considered in the ARQmechanisms for end-to-end delivery of data packets.

[0010] To this end as well as others, there is a need for a method andapparatus to efficiently control flow of data in a communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The features, objects, and advantages of the present inventionwill become more apparent from the detailed description set forth belowwhen taken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

[0012]FIG. 1 illustrates a communication system capable of operating inaccordance with various embodiments of the invention.

[0013]FIG. 2 illustrates the forward link channel structure in awireless data communication system.

[0014]FIG. 3 illustrates the reverse link channel structure in awireless data communication system.

[0015]FIG. 4 illustrates decoding of an acknowledgment channel data bitin accordance with various received energy thresholds.

[0016]FIG. 5 illustrates a stack of protocol layers for controlling flowof data in a communication system.

[0017]FIG. 6 illustrates a table for selecting a maximum number ofallowed transmission slots for communication of a packet of data at aselected data rate.

[0018]FIG. 7 illustrates early and normal terminations of transmitting apacket of data at the physical layer.

[0019]FIG. 8 illustrates an exemplary flow of radio link protocol layerpackets of data;

[0020]FIG. 9 illustrates a flow diagram of various steps for determiningan extra retransmission of a physical layer packet of data in accordancewith various aspects of the invention;

[0021]FIG. 10 illustrates a flow diagram of various steps for ignoring aradio link negative acknowledgment in accordance with various aspects ofthe invention;

[0022]FIG. 11 illustrates a receiver system for receiving and decodingvarious channels, and capable of operating in accordance with variousaspects of the invention;

[0023]FIG. 12 illustrates a transmitter system for transmitting variouschannels, and capable of operating in accordance with various aspects ofthe invention; and

[0024]FIG. 13 illustrates a transceiver system for receiving andtransmitting various channels, and capable of operating in accordancewith various aspects of the invention.

[0025]FIG. 14 illustrates a method of control flow implementing powerboosting.

[0026]FIG. 15 is a layering architecture consistent with a communicationsystem supporting High Rate Packet Data (HRPD) transmissions.

[0027]FIG. 16 is a base station transceiver supporting one embodiment ofthe present invention.

[0028]FIG. 17 is a channel structure in a wireless communication system.

[0029]FIG. 18 illustrates use of different Walsh codes to identify eachuser on a feedback channel.

[0030]FIG. 19 is a scheme for providing multiple negativeacknowledgments for a data packet wherein the negative acknowledgmentsare significant in a layer above the physical layer.

[0031]FIG. 20 is an example of transmission of a packet of data.

[0032]FIG. 21 illustrates incremental redundancy in transmission ofsubpackets.

[0033]FIG. 22 is a table corresponding rate and payload information toRRI codes.

[0034]FIG. 23 illustrates sequential transmission of RRI in timingdiagram form.

[0035]FIG. 24 illustrates a sequence detection window of subpackets in atransmission.

[0036]FIG. 25 illustrates a sequence detection window of subpackets in atransmission.

[0037]FIG. 26 is trellis diagram illustrating a method for decoding.

[0038]FIG. 27 is a method for decoding in a system supportingincremental redundancy of subpacket transmissions.

DETAILED DESCRIPTION

[0039] The word “exemplary” is used herein to mean “serving as anexample, instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

[0040] An HDR subscriber station, referred to herein as an accessterminal (AT), may be mobile or stationary, and may communicate with oneor more HDR base stations, referred to herein as modem pool transceivers(MPTs). An access terminal transmits and receives data packets throughone or more modem pool transceivers to an HDR base station controller,referred to herein as a modem pool controller (MPC). Modem pooltransceivers and modem pool controllers are parts of a network called anaccess network. An access network transports data packets betweenmultiple access terminals. The access network may be further connectedto additional networks outside the access network, such as a corporateintranet or the Internet, and may transport data packets between eachaccess terminal and such outside networks. An access terminal that hasestablished an active traffic channel connection with one or more modempool transceivers is called an active access terminal, and is said to bein a traffic state. An access terminal that is in the process ofestablishing an active traffic channel connection with one or more modempool transceivers is said to be in a connection setup state. An accessterminal may be any data device that communicates through a wirelesschannel or through a wired channel, for example using fiber optic orcoaxial cables. An access terminal may further be any of a number oftypes of devices including but not limited to PC card, compact flash,external or internal modem, or wireless or wireline phone. Thecommunication link through which the access terminal sends signals tothe modem pool transceiver is called a reverse link. The communicationlink through which a modem pool transceiver sends signals to an accessterminal is called a forward link.

[0041] Generally stated, various aspects of the invention provide forefficient use of communication resources in a communication system byefficiently determining the need for one more transmission of a physicallayer data packet on the forward link based on repeating the decoding ofthe previously received signal of the acknowledgment channel. Repeatingthe decoding process may involve use of different decoding thresholds.Subsequently, the retransmission of the physical layer packet mayinclude use of temporal diversity. Various techniques of temporaltransmission diversity are well known. One or more exemplary embodimentsdescribed herein are set forth in the context of a digital wireless datacommunication system. While use within this context is advantageous,different embodiments of the invention may be incorporated in differentenvironments or configurations. In general, the various systemsdescribed herein may be formed using software-controlled processors,integrated circuits, or discrete logic. The data, instructions,commands, information, signals, symbols, and chips that may bereferenced throughout the application are advantageously represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or a combination thereof. In addition, theblocks shown in each block diagram may represent hardware or methodsteps.

[0042] More specifically, various embodiments of the invention may beincorporated in a wireless communication system operating in accordancewith the Code Division-Multiple Access (CDMA) technique which has beendisclosed and described in various standards published by theTelecommunication Industry Association (TIA) and other standardsorganizations. Such standards include the TIA/EIA-95 standard,TIA/EIA-IS-2000 standard, IMT-2000 standard, UMTS and WCDMA standard. Asystem for communication of data is also detailed in the “TIA/EIA/IS-856cdma2000 High Rate Packet Data Air Interface Specification.” A copy ofthe standards may be obtained by writing to TIA, Standards andTechnology Department, 2500 Wilson Boulevard, Arlington, Va. 22201,United States of America. The standard generally identified as UMTSstandard, incorporated by reference herein, may be obtained bycontacting 3GPP Support Office, 650 Route des Lucioles-Sophia Antipolis,Valbonne-France.

[0043]FIG. 1 illustrates a general block diagram of a communicationsystem 100 capable of operating in accordance with any of the CodeDivision Multiple Access (CDMA) communication system standards whileincorporating various embodiments of the invention. Communication system100 may be for communications of data, or data and voice. Generally,communication system 100 includes a base station 101 that providescommunication links between a number of mobile stations, such as mobilestations 102-104, and between the mobile stations 102-104 and a publicswitch telephone and data network 105. The mobile stations in FIG. 1 maybe referred to as data Access Terminals (AT) and the base station asdata Access Network (AN) without departing from the main scope andvarious advantages of the invention. Base station 101 may include anumber of components, such as a base station controller and a basetransceiver system. For simplicity, such components are not shown. Basestation 101 may be in communication with other base stations, forexample base station 160. A mobile switching center (not shown) maycontrol various operating aspects of the communication system 100 and inrelation to communications over a back-haul 199 between network 105 andbase stations 101 and 160. Base station 101 communicates with eachmobile station that is in its coverage area via a forward link signaltransmitted from base station 101. The forward link signals targeted formobile stations 102-104 may be summed to form a forward link signal 106.Each of the mobile stations 102-104 receiving forward link signal 106decodes the forward link signal 106 to extract the received information.Base station 160 may also communicate with the mobile stations that arein its coverage area via a forward link signal transmitted from basestation 160. Mobile stations 102-104 communicate with base stations 101and 160 via corresponding reverse links. Each reverse link is maintainedby a reverse link signal, such as reverse link signals 107-109 formobile stations 102-104, respectively. The reverse link signals 107-109,although may be targeted for one base station, may be received at otherbase stations.

[0044] Base stations 101 and 160 may be simultaneously communicating toa common mobile station. For example, mobile station 102 may be in closeproximity of base stations 101 and 160, which can maintaincommunications with both base stations 101 and 160. On the forward link,base station 101 transmits on forward link signal 106, and base station160 on the forward link signal 161. On the reverse link, mobile station102 transmits on reverse link signal 107 to be received by both basestations 101 and 160. For transmitting a packet of data to mobilestation 102, one of the base stations 101 and 160 may be selected totransmit the packet of data to mobile station 102. On the reverse link,both base stations 101 and 160 may attempt to decode the traffic datatransmission from the mobile station 102. The data rate and power levelof the reverse and forward links may be maintained in accordance withthe channel condition between the base station and the mobile station.The reverse link channel condition may not be the same as the forwardlink channel condition. The data rate and power level of the reverselink and forward link may be different. One ordinary skilled in the artmay recognize that the amount of data communicated in a period of timevaries in accordance with the communication data rate. A receiver mayreceive more data at high data rate than low data rate during the sameperiod of time. Moreover, the rate of communications between the usersmay also change. A receiver may receive more data at high rate ofcommunications than low rate of communications during the same period oftime. Moreover, when communication of a packet of data takes more thanone transmission, the effective amount of data communicated over aperiod of time is reduced. Therefore, the throughput of thecommunication between a mobile station and a base station may changefrom time to time based on the channel condition. In accordance with oneor more aspects of the invention, efficient use of communicationresources in communication system 100 may be made by determining theneed for one more retransmission of a physical layer data packet, afterbeing detected as a lost data packet, based on the throughput of thecommunication between the base station and the mobile station.

[0045] In accordance with various aspects of the invention, incommunication system 100, re-transmitting a lost packet of data at leastone more time after detecting its loss is based on whether a determinedthroughput of a communication link between a source user and adestination user is above a throughput threshold. The source user may bea base station, such as base station 101 or 160, and the destinationuser may be any of the mobile stations 102-104. After establishing aforward link communication, loss of the packet of data may be detectedby the mobile station. The throughput of the forward link communicationmay be determined in terms of the communication data rate, rate ofcommunications, number of retransmissions used between the source userand the destination user, or any combination thereof. The retransmissionmay include use of transmission diversity. Moreover, the reception ofthe retransmission may include receive diversity. When the throughput isabove the threshold, the possibility of receiving the lost packet ofdata through the retransmission is higher due to a favorable throughputchannel condition. Therefore, when the retransmission does not takeplace due to failure of the throughput for being above the threshold,the communication resources are conserved by being used efficiently.Moreover, when the retransmission takes place, the delay in flow of dataamong various protocol layers is minimized by providing a timelysuccessful reception of the lost packet of data during favorablethroughput channel condition.

[0046]FIG. 2 illustrates a forward channel structure 200 in accordancewith an embodiment that may be used for the channel structure of thecommunications on the forward link. Forward channel structure 200 mayinclude a pilot channel 201, a medium access control (MAC) channel 202,a traffic channel 203 and a control channel 204. The MAC channel 202 mayinclude a reverse activity channel 206 and a reverse power controlchannel 207. Reverse activity channel 206 is used to indicate theactivity level on the reverse link. Reverse power control channel 207 isused to control the power at which a mobile station can transmit on thereverse link.

[0047]FIG. 3 illustrates, in accordance with an embodiment, a reversechannel structure 300 that may be used for the channel structure of thecommunications on the reverse link. Reverse channel structure 300includes an access channel 350 and a traffic channel 301. Access channel350 includes a pilot channel 351 and a data channel 353. Traffic channel301 includes a pilot channel 304, a MAC channel 303, an acknowledgment(ACK) channel 340 and a data channel 302. The MAC channel 303 includes areverse link data rate indicator channel 306 and a Data Rate Control(DRC) channel 305. Reverse Rate Indicator (RRI) channel 306 is used forindicating the rate at which a mobile station is currently transmitting.Data Rate Control (DRC) channel 305 indicates a data rate that a mobilestation is capable of receiving on the forward link. For example, theDRC value 0×3 may indicate the data rate 153.6 kbps. Moreover, thesystem may require a predefined and limited number of retransmissions ofa physical layer packet of data that possibly can take place. Forexample, at the data rate 153.6 kbps, the system allows up to 3retransmissions of the same packet of data after the initialtransmission, resulting in a total of four transmissions. If thephysical layer packet of data is not decoded properly after the initialtransmission, as indicated by the ACK channel 340 in the reverse link,the transmitter may send the same packet of data one more time. Theretransmission may continue up to three times. The transmitter does nottransmit the same packet of data more than four times, one initial timeand three retransmissions, when the data rate is at 153.6 kbps. ACKchannel 340 is used for communicating whether a received physical layerdata packet has been decoded successfully at a mobile station. When apacket of data is lost, even after the maximum allowed retransmissions,in accordance with various aspects of the invention, in communicationsystem 100, re-transmitting the lost packet of data at least one moretime may be based on whether a determined throughput of thecommunication link between the mobile station and serving base stationis above a throughput threshold.

[0048] ACK channel 340 is transmitted by a mobile station. Transmissionon ACK channel 340 may indicate either a negative acknowledgment (NAK)or a positive acknowledgement (ACK). The mobile station may transmit aNAK message as indicated by a single NAK bit to the serving base stationuntil a received physical layer data packet is successfully decoded. Thephysical layer data packet may be successfully decoded before themaximum number of allowed retransmissions. If a received packet of datais correctly decoded, the mobile station sends an ACK message asindicated by a single ACK bit on the ACK channel 340 to the serving basestation. The ACK channel 340 may use a Binary Phase Shift Keying (BPSK)modulation transmitting a positive modulation symbol for a positiveacknowledgment and a negative modulation symbol for a negativeacknowledgment. In a transmitter described in IS-856 standard, theACK/NAK bit passes and repeats through a BPSK modulator. The BPSKmodulator modulates the ACK/NAK bit, and the resulting signal is Walshcovered in accordance with an assigned Walsh code. In one embodiment,the received signal of the ACK channel 340 may be compared against apositive and negative voltage threshold. If the received signal levelmeets the positive voltage threshold, an ACK message is consideredreceived on the ACK channel 340. If the signal level meets the negativevoltage threshold, a NAK message is considered received on the ACKchannel 340.

[0049] Referring to FIG. 4, decoding of ACK channel 340 may beillustrated. The resulting signal may be compared against a positivethreshold 401 and a negative threshold 402. If the signal is above thepositive threshold 401, an ACK bit is considered received on the ACKchannel 340. If the signal is below the negative threshold 402, a NAKbit is considered received on the ACK channel 340. The positive andnegative thresholds 401 and 402 may not be at the same level. As such,an erasure region 403 may be created between the positive and negativethresholds 401 and 402. If the resulting demodulated signal falls in theerasure region 403, the receiving base station may not be able todetermine whether an ACK or NAK bit has been transmitted from the mobilestation on ACK channel 340.

[0050] The ARQ mechanism may have a few problems when the received ACKchannel 340 signal is in the erasure region 403. If the erasure isinterpreted as an ACK, when in fact a NAK is transmitted from the mobilestation, the base station stops transmitting the remaining number ofallowed retransmissions of the physical layer data packet. As a result,the mobile station would not receive the physical layer packet of dataand may rely on a retransmission mechanism of a higher level protocollayer, such as a Radio Link Protocol (RLP) layer, to recover the lostpacket of data. However, the delay in receiving the packet of data andutilization of the communication resources are higher at the RLP layerthan the physical protocol layer. One of the measured system qualitiesmay be the certainty associated with proper and on time delivery of adata packet to a mobile station. To avoid such a problem, in oneembodiment, the process of decoding the ACK channel may be biased towarddetecting a NAK by interpreting an erasure as a NAK. If the mobilestation in fact has transmitted an ACK and the serving base stationdetects an erasure, interpreting the erasure as a NAK allows the basestation to continue the transmission of the physical layer data packetfor at least one more time of the remaining number of times, when infact any retransmission of the data packet is not necessary. Such aretransmission, even though may not be necessary, in fact may achieveefficient use of the communication resources with minimal delay fordelivery of data packets.

[0051] The flow of data between two end points may be controlled viaseveral protocol layers. An exemplary stack of the protocol layers 500is shown in FIG. 5 for controlling flow of data between two end points.For example, one end point may be a source connected to Internet throughthe network 105. The other end point may be a data processing unit suchas a computer coupled to a mobile station or integrated in a mobilestation. The protocol layers 500 may have several other layers or eachlayer may have several sub-layers. A detailed stack of protocol layersis not shown for simplicity. The stack of protocol layers 500 may befollowed for flow of data in a data connection from one end point toanother. At the top layer, a TCP layer 501 controls the TCP packets 506.TCP packets 506 may be generated from a much larger application datamessage/packet. The application data may be partitioned into several TCPpackets 506. The application data may include text message data, videodata, picture data or voice data. The size of the TCP packets 506 may bedifferent at different times. At the Internet Protocol layer (IP) layer502, a header is added to the TCP packets 506 to produce data packet507. The header may include a destination address, among other fields,for proper routing of the packets to the appropriate destination node.At a point-to-point protocol (PPP) layer 503, PPP header and trailerdata are added to data packet 507 to produce data packet 508. The PPPdata may identify the point-to-point connection addresses for properrouting of a packet of data from a source connection point to adestination connection point. The PPP layer 503 may pass data for morethan one TCP layer protocol connected to different ports.

[0052] A radio link protocol (RLP) layer 504 provides a mechanism forretransmission and recovery of data packets erased over the air.Although TCP has a retransmission scheme for reliable data transfer, therate of losing packets of data over the air may result in overall poorTCP performance. Implementing an RLP mechanism at a lower layereffectively lowers the rate of losing TCP packets at the TCP level. AtRLP layer 504, the data packet 508 is divided into several RLP packetsin a group of RLP packets 509A-N. Each RLP packet of the group of theRLP packets 509A-N is processed independently and assigned a sequencenumber. The sequence number is added to the data in each RLP packet foridentifying the RLP packet among the RLP packets in the group of the RLPpackets 509A-N. One or more of the RLP packets in the group of the RLPpackets 509A-N is placed into a physical layer packet of data 510. Aphysical layer 505 controls the channel structure, frequency, poweroutput, and modulation specification for data packet 510. The datapacket 510 is transmitted over the air. The size of the payload of thepacket of data 510 may vary depending on the rate of transmission.Therefore, the size of data packet 510 may be different from time totime based on the channel condition and the selected communication datarate.

[0053] At a receiving destination, the physical layer data packet 510 isreceived and processed. The ACK channel 340 may be used foracknowledging success/failure in reception of physical layer data packet510 transmitted from a base station to a mobile station. If the physicallayer data packet 510 is received without error, the received packet 510is passed on to RLP layer 504. The RLP layer 504 attempts to reassemblethe RLP packets in the group of the RLP packets 509A-N from the receivedpackets of data. In order to reduce the packet error rate seen by TCP501, the RLP layer 504 implements an automatic retransmission request(ARQ) mechanism by requesting retransmission for the missing RLPpackets. The RLP protocol re-assembles the group of the RLP packets509A-N to form a complete PPP packet 508. The process may take some timeto completely receive all the RLP packets in the group of the RLPpackets 509A-N. Several physical layer data packets 510 may be needed tocompletely send all the RLP packets in the group of the RLP packets509A-N. When an RLP packet of data is received out of sequence, the RLPlayer 504 sends an RLP negative acknowledgement (NAK) message on asignaling channel to the transmitting base station. In response, thetransmitting base station retransmits the missing RLP data packet.

[0054] Referring to FIG. 6, a table 600 depicts the DRC value of the DRCchannel 305, the corresponding data rate, and the corresponding maximumnumber of allowed transmissions of a physical layer packet of data. Forexample, for the DRC value 0×3, the data rate is 153.6 kbps and thecorresponding maximum number of allowed transmissions is four timeslots. Transmission of a physical layer packet of data may have an earlytermination or a normal termination. With early termination, thephysical layer packet of data has been decoded properly at the receiverand the transmitting source has received an ACK message on the ACKchannel 340 corresponding to the received physical layer packet of data.With normal termination, the transmitter has exhausted using all theallowed transmissions slots of the physical layer packet of data withoutreceiving a corresponding ACK message on the ACK channel 340.

[0055] Referring to FIG. 7, an early termination and normal terminationfor transmitting a physical layer packet of data are illustrated for thecase of DRC value 0×3 corresponding to 153.6 kbps data rate. For anearly termination in transmission of a physical layer packet of data forthe case of DRC value 0×3 corresponding to 153.6 kbps data rate, at atime slot 702 prior to the first transmission of the physical layerpacket of data, a DRC value is received on the DRC channel 305. The DRCvalue is used to determine the communication data rate and the maximumnumber of allowed retransmissions for the physical layer packet of data.At time slot “n” of the time slots 701, the first transmission of thephysical layer packet of data may take place. During the next three timeslots, “n+1, n+2, and n+3”, the transmitter expects to receive an ACK orNAK on the ACK channel 340. Time slots 703 show that a NAK is receivedbefore the time slot “n+4”. The first retransmission of the physicallayer packet of data takes place during the time slot “n+4”. Thetransmitter waits three more time slots to receive an ACK or NAK on theACK channel 340. Time slots 703 show that a NAK is received before thetime slot “n+8”. The second retransmission of the physical layer packetof data takes place during the time slot “n+8”. For data rate 153.6kbps, the transmitter is allowed to make one more transmission of thesame physical layer packet of data. The transmitter waits three moretime slots to receive an ACK or NAK message on the ACK channel 340.Before the time slot “n+12”, an ACK message is received on the ACKchannel 340. Therefore, the transmitter makes an early termination ofthe transmission of the physical layer packet of data before exhaustingall the allowed transmission slots. The time slot “n+12” may be used fortransmission of another physical layer packet of data.

[0056] For a normal termination of transmitting a physical layer packetof data for the case of DRC value 0×3 corresponding to 153.6 kbps datarate, at a time slot 802 prior to the first transmission of the physicallayer packet of data, a DRC value is received on the DRC channel 305.The DRC value is used to determine the communication data rate and themaximum number of allowed retransmissions for the physical layer packetof data. At time slot “n” of the time slots 801, the first transmissionof the physical layer packet of data may take place. During the nextthree time slots, “n+1, n+2, and n+3”, the transmitter expects toreceive an ACK or NAK on the ACK channel 340. Time slots 803 may showthat a NAK is received before the time slot “n+4”. The firstretransmission of the physical layer packet of data takes place duringthe time slot “n+4”. The transmitter waits three more time slots toreceive an ACK or NAK on the ACK channel 340. Time slots 803 may showthat a NAK is received before the time slot “n+8”. The secondretransmission of the physical layer packet of data takes place duringthe time slot “n+8”. For data rate 153.6 kbps, the transmitter isallowed to make one more transmission of the same physical layer packetof data. The transmitter waits three more time slots to receive an ACKor NAK on the ACK channel 340. Before the time slot “n+12”, a NAKmessage is received on the ACK channel 340. Therefore, the transmittermakes the last allowed transmission of the physical layer packet of dataon the time slot “n+12”, and concludes the normal termination oftransmitting the physical layer packet of data after exhausting all theallowed transmissions of the physical layer packet of data.

[0057] Generally, the transmitter is not required to monitor the ACKchannel 340 for detecting whether the last transmission has beenreceived in either success or failure. The physical layer packet may notbe successfully received at the mobile station following a normaltermination. In this case, the re-assembly of RLP packets of data at theRLP layer 504 would not be complete. As a result, the RLP layer 504makes a request for retransmission of the RLP packet of data by sendingan RLP NAK signaling message.

[0058] In accordance with various aspects of the invention, after anormal termination of transmission of a physical layer packet of data,the base station may monitor the ACK channel 340 and if a NAK isreceived, it may repeat decoding the previously received signal of ACKchannel 340 with adjusted ACK/NAK thresholds 401 and 402. Theadjustments of the ACK/NAK thresholds 401 and 402 are made such that thedecoding is biased toward detection of an ACK message. Such a bias maybe created by treating the erasures as ACKs without changing the levelof the NAK threshold 402 from the previously used level or by selectinga different threshold altogether.

[0059] Generally, an ARQ mechanism through the RLP layer takes sometime, which includes the round trip delay between the mobile station andthe base station as well as the processing delays. Referring to FIG. 8,a message flow 800 is shown to provide an exemplary flow of RLP packetsof data. The RLP packets with sequence numbers “01” to “07” are sentfrom a source to a destination, for example. The source and destinationmay be, respectively, either a base station and a mobile station or amobile station and a base station. At the RLP layer 504, the RLP packets509A-N are accumulated to complete the packet 508. Once all the RLPpackets are received, the RLP packets 509A-N are passed on to a higherlevel. At the physical layer 505, the communication of the physicallayer data packet 510 also includes an ARQ method through the use of theACK channel 340. One or more RLP packets may be combined into a commonpayload and sent on one physical layer data packet 510. In the exemplarymessage flow 800, the RLP packet identified as RLP packet “03”, forexample, does not get to the destination. The failure may be due to manyfactors including erasure on the radio link between the source and thedestination. In this case, the normal termination of transmitting thephysical layer packet of data that includes the RLP packet of data “03”may have taken place. After the destination receives RLP packet “04”,the RLP layer 504 detects an out of sequence reception of the RLPpackets. The RLP layer 504 sends an RLP NAK message identifying RLPpacket “03” as missing in the communication. The processing fordetection of a missing RLP packet of data, the propagation of the RLPNAK message, and the subsequent RLP retransmission may take some time.The duration may be long enough to allow one quick retransmission of thephysical layer of packet of data, beyond the maximum allowed number ofretransmissions, for an earlier recovery. If this additionalretransmission, in accordance with various aspects of the invention, issuccessful before transmitting an RLP NAK message, the RLP NAK messagemay not be transmitted.

[0060] When the RLP NAK message is transmitted, the RLP layer 504 startsa timer. The timer counts the lapsed amount of time since sending theRLP NAK message. If the timer expires, for example after 500 msec,before receiving the missing RLP packet “03”, the destination RLP 504may assume that the retransmission of the missing RLP packet has failed.Once the missing RLP packet “03” is received, the timer terminates. Thecorrectly received packets of data may be collected in a storage unit toform a group of packets of data. Therefore, the processing for detectionand retransmission of a missing RLP packet of data may take some time.The duration may be sufficiently long so as to allow one moreretransmission of the physical layer of packet of data beyond themaximum allowed number of retransmissions. If this additionalretransmission is successful before expiration of the timer, the timermay terminate due to receiving the retransmission of the physical layerpacket of data successfully. It is possible that the RLP NAK message wassent before the extra physical layer retransmission was successfullyreceived. In such a case either the base station may choose to ignorethe received RLP NAK message or it may perform the RLP retransmission ofthe missing packet, which will be discarded as a duplicate at the mobilestation. It is possible that the extra physical layer retransmission mayend in a failed normal termination. In this case, the usual RLPretransmission mechanism may provide the recovery of the lost packet.

[0061]FIG. 9 illustrates a method 900 for an ARQ mechanism. At step 901,the transmitter may determine the DRC value for transmission of aphysical layer packet of data. The DRC value may be determined bydecoding the DRC channel 305. At step 902, the maximum number of timeslots allowed for transmission of the physical layer packet of data maybe determined by referring to table 600 in FIG. 6. At step 903, thetransmitter may detect a normal termination of the transmission of thephysical layer packet of data over the maximum number of allowed timeslots without receiving a subsequent ACK on the ACK channel 340. At step905, the ACK and NAK thresholds 401 and 402 may be adjusted to biastowards detection of an ACK message. At step 906, the signal of thepreviously received ACK channel 340 is re-decoded using the adjustedthresholds to determine the bit on the ACK channel 340. If there-decoding produces a NAK bit, the physical layer packet of data istransmitted one more round, at step 907. This additional round oftransmissions includes a number of transmissions up to maximum allowedslots according to table 600 in FIG. 6 depending on the requested DRC atthe time of start of retransmission. At this time, the transmitter maydetermine a new DRC value by decoding the DRC channel 305 to determinethe maximum number of time slots allowed for transmission of thephysical layer packet of data. The channel condition may have changedduring the process. The new round of transmissions may begin after somedelay. The delay may be necessary to allow a de-correlation in thechannel condition. When the de-correlation of the channel conditiontakes place, the probability that the transmission of physical packet ofdata is successful is higher. The new round of transmissions may be inaccordance of a newly received DRC value; thus, the number of allowedretransmissions may be different in this round of transmissions. At step910, the next physical layer packet of data is transmitted. The lastretransmission at step 907 may arrive and be decoded at the destinationproperly, and possibly eliminating a need for re-transmitting an RLPpacket of data. As such, a delayed ARQ (DARQ) at the physical layer isvery helpful for efficient communications of data. Channel correlationsimply means that if a packet got erased in a slot, it is quite likelythat it would get erased again if it were retransmitted immediately.This is particularly a concern in slow fading channel conditions. Thus,it is necessary to temporally de-correlate the retransmission from thelost transmission. This implies that the retransmission should occur atthe earliest time that allows sufficient channel de-correlationfollowing the lost transmission. The “Delayed ARQ (DARQ)” is, therefore,used. Simulation studies indicate that a delay of 10 to 20 msec issufficient, while other delayed time periods are also possible, meetsthe requirements.

[0062] DARQ in accordance with various aspects of the invention mayresult in significant performance gains for high throughput users undersome traffic conditions. The interactions between TCP and the lowerlayers in a system may result in significant throughput loss for someusers under typical (1% packet error rate (PER)) operating conditions.This loss can be attributed to several factors. A forward link lossleading to a RLP retransmission causes a delay in the receipt of the TCPsegment affected by the loss, as well as the subsequent TCP segmentswhich were received, but could not be delivered immediately due to thesequential delivery requirement of RLP. This would delay the generationof TCP ACK at the receiver. When the lost packet is recovered due to RLPretransmission, a burst of packets would be delivered to the TCP layer,which would in turn generate a burst of TCP ACK, which may temporarilyoverload the reverse link. The end result is that the TCP sender maytime out, and thus causing a retransmission of packets, which have beensuccessfully received in the first place. Moreover, the congestionwindow at the TCP sender is reduced to its slow start value (typicallyone TCP segment) and can take some time to recover before a steady flowof packets can be achieved which may lead to “starvation” of the forwardlink.

[0063] The problems described above can be alleviated to a great degree,if an extra physical layer retransmission is performed on the forwardlink fairly quickly according to various embodiments. The extraretransmission provides additional robustness. The quickness of theretransmission will help in reducing the delay thus possibly eliminatingthe TCP sender timeout. Moreover, the quick retransmission will reducethe delay variability seen by the TCP sender, which may lead to improvedperformance. There are other by-products of such a scheme such as in thecase when the last byte in a forward link transmission gets lost. Sincethis won't generate a NAK from the mobile, the base station maintains aflush timer to cause a forced retransmission. DARQ would result in anautomatic retransmission in this case, and a flush timer may not benecessary.

[0064] Various aspects of the invention may be useful under manydifferent system conditions, including high throughput condition. Thehigh throughput condition occurs when the channel condition is veryfavorable for low error rate communications and possibly there are fewusers in the system. The additional retransmission may provide moregains for high throughput users than low throughput users. For lowthroughput users, it may result in extra overhead without any benefit.Therefore, to add an additional layer of control for various aspects ofthe invention, after step 903 and before step 905, the transmitter maydetermine the throughput of the user receiving the communication. If thethroughput is above a throughput threshold, the process moves to step905 to prepare for deciding whether one additional retransmission of thephysical layer packet of data may take place.

[0065] After normal termination of transmitting the physical layerpacket of data and before completing the extra transmission of thephysical layer packet of data, the RLP layer 504 may start and transmita RLP NAK message. If the RLP NAK message arrives along with an ACKindication on the ACK channel 340 for proper reception of the extratransmission made after the normal termination, the RLP NAK may beignored in accordance with various aspects of the invention. Variousaspects of the invention may be more apparent by referring to flowdiagram 1010 shown in FIG. 10. At step 1011, an ACK on the ACK channel340 is received. The ACK is related to the physical layer packet of dataretransmitted after the failed normal termination of the firsttransmission. At step 1012, a RLP NAK message may also be received. TheRLP NAK message may be associated with an RLP packet of data that wasincluded in the physical layer packet of data. Such a detection may bemade at step 1013. At step 1014, the received RLP NAK message may beignored and the controller may consider the RLP packet of data receivedproperly at the destination based on the received ACK bit on the ACKchannel 340. The mobile station may delay transmitting the RLP NAKmessage after detecting that the last transmission of the physical layerpacket of data should have taken place, and while not receiving the lasttransmission.

[0066]FIG. 11 illustrates a block diagram of a receiver 1200 used forprocessing and demodulating the received CDMA signal. Receiver 1200 maybe used for decoding the information on the reverse and forward linkssignals. Received (Rx) samples may be stored in RAM 1204. Receivesamples are generated by a radio frequency/intermediate frequency(RF/IF) system 1290 and an antenna system 1292. The RF/IF system 1290and antenna system 1292 may include one or more components for receivingmultiple signals and RF/IF processing of the received signals for takingadvantage of the receive diversity gain. Multiple received signalspropagated through different propagation paths may be from a commonsource. Antenna system 1292 receives the RF signals, and passes the RFsignals to RF/IF system 1290. RF/IF system 1290 may be any conventionalRF/IF receiver. The received RF signals are filtered, down-converted anddigitized to form RX samples at base band frequencies. The samples aresupplied to a demultiplexer (demux) 1202. The output of demux 1202 issupplied to a searcher unit 1206 and finger elements 1208. A controlunit 410 is coupled thereto. A combiner 1212 couples a decoder 1214 tofinger elements 1208. Control system 1210 may be a microprocessorcontrolled by software, and may be located on the same integratedcircuit or on a separate integrated circuit. The decoding function indecoder 1214 may be in accordance with a turbo decoder or any othersuitable decoding algorithms.

[0067] During operation, received samples are supplied to demux 1202.Demux 1202 supplies the samples to searcher unit 1206 and fingerelements 408. Control system 1210 configures finger elements 1208 toperform demodulation and despreading of the received signal at differenttime offsets based on search results from searcher unit 1206. Theresults of the demodulation are combined and passed to decoder 1214.Decoder 1214 decodes the data and outputs the decoded data. Despreadingof the channels is performed by multiplying the received samples withthe complex conjugate of the PN sequence and assigned Walsh function ata single timing hypothesis and digitally filtering the resultingsamples, often with an integrate and dump accumulator circuit (notshown). Such a technique is commonly known in the art. Receiver 1200 maybe used in a receiver portion of base stations 101 and 160 forprocessing the received reverse link signals from the mobile stations,and in a receiver portion of any of the mobile stations for processingthe received forward link signals.

[0068]FIG. 12 illustrates a block diagram of a transmitter 1300 fortransmitting the reverse and forward link signals. The channel data fortransmission are input to a modulator 1301 for modulation. Themodulation may be according to any of the commonly known modulationtechniques such as QAM, PSK or BPSK. The data is encoded at a data ratein modulator 1301. The data rate may be selected by a data rate andpower level selector 1303. The data rate selection may be based onfeedback information received from a receiving destination. Thereceiving destination may be a mobile station or a base station. Thefeedback information may include the maximum allowed data rate. Themaximum allowed data rate may be determined in accordance with variouscommonly known algorithms. The maximum allowed data rate very often isbased on the channel condition, among other considered factors. The datarate and power level selector 1303 accordingly selects the data rate inmodulator 1301. The output of modulator 1301 passes through a signalspreading operation and amplified in a block 1302 for transmission froman antenna 1304. The data rate and power level selector 1303 alsoselects a power level for the amplification level of the transmittedsignal in accordance with the feedback information. The combination ofthe selected data rate and the power level allows proper decoding of thetransmitted data at the receiving destination. A pilot signal is alsogenerated in a block 1307. The pilot signal is amplified to anappropriate level in block 1307. The pilot signal power level may be inaccordance with the channel condition at the receiving destination. Thepilot signal is combined with the channel signal in a combiner 1308. Thecombined signal may be amplified in an amplifier 1309 and transmittedfrom antenna 1304. The antenna 1304 may be in any number of combinationsincluding antenna arrays and multiple input multiple outputconfigurations.

[0069]FIG. 13 depicts a general diagram of a transceiver system 1400 forincorporating receiver 1200 and transmitter 1300 for maintaining acommunication link with a destination. The transceiver 1400 may beincorporated in a mobile station or a base station. A processor 1401 maybe coupled to receiver 1200 and transmitter 1300 to process the receivedand transmitted data. Various aspects of the receiver 1200 andtransmitter 1300 may be common, even though receiver 1200 andtransmitter 1300 are shown separately. In one aspect, receiver 1200 andtransmitter 1300 may share a common local oscillator and a commonantenna system for RF/IF receiving and transmitting. Transmitter 1300receives the data for transmission on input 1405. Transmit dataprocessing block 1403 prepares the data for transmission on a transmitchannel. Received data, after being decoded in decoder 1214, arereceived at processor 1401 at an input 1404. Received data are processedin received data processing block 1402 in processor 1401. The processingof the received data generally includes checking for error in thereceived packets of data. For example, if a received packet of data haserror at an unacceptable level, the received data processing block 1402sends an instruction to transmit data processing block 1403 for making arequest for retransmission of the packet of data. The request istransmitted on a transmit channel. Various channels, such as the ACKchannel 340, may be used for the retransmission process. As such, thecontrol system 1210 and processor 1401 may be used for performingvarious aspects of the invention including various steps described inrelation to flow diagrams 900. A receive data storage unit 1480 may beutilized to store the received packets of data. Various operations ofprocessor 1401 may be integrated in a single or multiple processingunits. The transceiver 1400 may be connected to another device. Thetransceiver 1400 may be an integral part of the device. The device maybe a computer or operates similar to a computer. The device may beconnected to a data network, such as Internet. In case of incorporatingthe transceiver 1400 in a base station, the base station through severalconnections may be connected to a network, such as Internet.

[0070] For a communication system incorporating a hybrid ARQ mechanismusing incremental redundancy, the data generated by a source may bepresented as a sequence of physical-layer packets. At the source, eachphysical-layer packet is encoded into a finite number of subpackets insuch a way that the destination (i.e., receiver) of the packet maypotentially decode a packet without receiving all the sub-packets. Notethe finite number of subpackets may not be distinct. In one scenario,different subpackets may actually be copies of each other. This is donewhen each subpacket contains symbols encoded at a sufficiently low coderate. In another scenario, a given subpacket may contain symbols encodedat a high code rate, wherein different subpackets contain differentencoded symbols. In this scenario, the combination of multiplesubpackets leads to a lower code rate than the code rate of any singlesubpacket. In particular, the packet may be encoded by a single channelcode of sufficiently low rate and the output of the encoder may be splitinto multiple, redundant fragments. Some fragments may be discarded andothers may be replicated to generate the required number of subpackets.In this way, the packet data is sent in installments.

[0071] According to one embodiment implementing a hybrid ARQ mechanism,physical layer packets installments are each slightly different, such aswherein systematic bits are consistent but parity bits may be different.At the destination or receiver, the installments of packets are thendecoded as a combination. This is in contrast to a simple ARQ scheme,wherein previously received packets are discarded and not considered indecoding the currently received packet. A maximum number of installmentsis allowed. The system also implements power control which seeks tocontrol the transmit power so as to maintain the Packet Error Rate (PER)after the maximum number of installments at a maximum allowable percent.In one embodiment the PER target is 1%.

[0072] It is a desire of high rate packet data systems, such as the1xEV-DO and/or 1xEV-DV systems, such as specified by cdma2000 andidentified by 3GPP2, to maximize data rate and thus throughput whilemaintaining the PER below or equal to a PER target value. Additionally,there is a desire to reduce the latency in transmission of data packets.

[0073] According to one embodiment, the system attempts to achieve thePER using less installments. In this way, the transmit power of theearly installments is increased so as to promote reception of thesystematic bits as early as possible. This mechanism is referred to aspower-boosting. For example, for a case wherein 4 installments areallowed, and a 1% PER specified, the system may power boost the first 2installments and ignore any NAK after that. In other words, if thetransmission is not successfully received on the power boostedinstallments, no further installments are transmitted, although the timeallocated for maximum number of installments may be reserved for thispacket installment. Note that the maximum number of installmentscorresponds to a maximum number of slots used for transmission of theinstallments.

[0074] When the power boost is not successful, the retransmission is nothandled further at the physical layer processing, but is handled at ahigher processing layer. For example, voice communications may be lost,as latency does not allow extended or delayed retransmission. The higherlayer may determine to resend a latency tolerant transmission byimplementing power boosting again. In one case, the higher layer, suchas the Medium Access Control (MAC) layer, may resend the installment ata later time or may reconfigure the data and repackage with other data.Note the MAC layer in particular monitors processing of packets in asystem. The MAC layer may resend later at a higher transmission rate incombination with other data. In this sense, a higher rate may refer topower boosted early slots, or the different coding and/or modulation.

[0075] Note that when the transmission is successfully received on thepower boosted installments, the system may use the next slot to begintransmission of the next packet. Alternatively, the system may reservethese slot(s) for the current packet and wait the transmission of thenext packet until after expiration of the maximum allowable time slots.Additionally note that a packet is typically distributed into multiplesubpackets. The concepts described herein are applicable to transmissionof a subpacket as well as transmission of a packet. The installments maybe for transmission of a subpacket or transmission of a packet.

[0076] The source of the physical-layer packet transmits one subpacketat a time on the primary channel, and waits for the destination to senda physical-layer ACK/NAK on the feedback channel, before sending thenext subpacket. The destination sends a physical-layer ACK for thepacket if it successfully decodes the packet with the help of thesubpackets received so far. The destination sends a physical-layer NAKfor the packet otherwise. (Not sending anything on the feedback channelmay be interpreted either as a ACK or NAK, depending on the conventionagreed upon by the two communication end-points.) Generally, thedestination sends a physical-layer ACK/NAK as quickly as possible,following the reception of a subpacket.

[0077] If the source detects an ACK on the feedback channel, it maydiscard all the remaining subpackets of the corresponding packet, andmay transmit the first subpacket or another physical-layer packet on theprimary channel. If the source detects a NAK on the feedback channel,the source transmits any unsent subpacket of the same packet, on theprimary channel. If the source detects a NAK but has no more subpacketsto send, the source declares a transmission failure and proceeds to sendsubpackets of another physical-layer packet.

[0078] Hybrid ARQ is typically used to combat unpredictable channelvariations during the transmission of a packet, as is typical inwireless communications. In such a system, the source may be powercontrolled by the destination, so that the subpackets are received withthe minimum power needed to achieve a (low-enough) target decodingfailure rate, after all the subpackets of the physical layer packet havebeen transmitted. The destination uses the feedback channel to issuepower control commands to the source, based on the quality of theprimary channel as measured by the destination, as well as the packetdecoding failure rate after the last subpacket has been received.

[0079] Typically, the packet is decoded by the receiver well before thelast subpacket is sent. The hybrid ARQ scheme allows efficienttransmission of data on an unpredictable, time-varying channel, withjust enough power and just enough redundancy, required for reliabledelivery at the destination.

[0080] Power Boost Technique

[0081] The worst case latency or transmission delay in an ARQ-basedsystem is typically defined as the time required to receive the lastsubpacket of a given packet at the destination. For some applications,such as real-time applications, the worst case ARQ-induced delay may beunacceptable, compromising the quality of the user experience. It isdesirable to reduce the worst-case latency for delay-sensitiveapplication, without causing undue burden or interference to theoperation of power control in the system. Generally, the source is awareof the delay-tolerance of the packet prior to transmission.

[0082] Generally, the source transmits the packet at the powerprescribed by power control operation for delay-tolerant packets, whichmay withstand the worst case ARQ delay. Alternate processing may beapplied to delay-sensitive packets. When the source wants to send adelay-sensitive packet, the source may power boost a portion of thesubpackets. In one example, a delay-sensitive packet contains Nsubpackets, wherein the delay-sensitive packet may only tolerate latencyassociated with the transmission of at most M subpackets, wherein M<N.In this case, the source transmits the subpackets associated with thedelay sensitive packet using a boosted power-level relative to thepower-level prescribed by power control. Pi is the transmit powerapplied to the ith sub-packet as prescribed by the power controlcommands. The source may actually send the ith subpacket, wherein i isan integer less than or equal to M, at a boosted power level Gi * Pi,wherein Gi represents the power-boost factor of the ith subpacket. Theith subpacket is transmitted only if the source detects a NAK from thedestination after the (i−1)th subpacket has been transmitted. If thesource detects a NAK after the Mth subpacket has been transmitted, thesource simply declares a transmission failure and moves on to the nextphysical-layer packet.

[0083] The power-boost factors Gi, for i=1 to M, is chosen appropriatelysuch that the probability of a decode failure subsequent to transmissionof the first M subpackets is equal to the power control target. Giventhat the power control ensures satisfactory reception of the packetafter the transmission of N subpackets, the system determines (forexample, through simulation) the power-boost values Gi that ensure (thesame level) satisfactory reception after the transmission of just Msubpackets. In particular, the system may use a common power boostvalue, wherein G1 is equal to G2 is equal to GM, etc., that achieves thedesired objective. To the first order G is set to a nominal valueGnom=(N/M), wherein N divided by M is greater than or equal to one, is areasonable choice for low data rate (or low spectral efficiency)transmission over static or fast fading channels. Here, a first ordervalue may be an ideal value or a value calculated using a simplisticsystem model. In practice, the power boost value may be somewhat largerthan the above nominal value to compensate for losses due to coding gainand time diversity.

[0084] By applying a well-chosen set of power-boost factors, the sourceof the packet can unilaterally control the worst-case transmissionlatency of a physical-layer packet, without impacting the effectivenessof power control or the reliability of packet transmission. Using anaverage power boost in excess of:

Gnom=(N/M)  (1)

[0085] may result in a (small) loss in coverage and/or system capacity,which reflects the price paid to minimize transmission latency on anoisy, time-varying channel. The power boost factors may be calculatedempirically. For a static channel if the number of power boostinstallments is reduced to half the maximum number of installments, thenthe transmit power may be doubled in the power boost installments. Byreducing the number of installments necessary for transmission of asubpacket, the effective data rate is increased significantly.

[0086]FIG. 14 illustrates a power boost mechanism performed at atransmission source according to one embodiment. The method 2000 startswhen a data packet is prepared for transmission. The data packetincludes a plurality of subpackets. The source determines the latencytolerance of the packet at step 2002. The latency tolerance informationis used to determine the power boosting scenario, including number ofinstallments to power boost as well as the power boost factors. At step2004, the source determines a maximum number installments for thesubpacket. The source then determines a number of slots for applicationof power boosting at step 2006. The source also determines the powerboost factor for each of those installments. As each installment istransmitted in a slot, the power boost factor may be considered asapplied to an installment in a given slot. Note that the power boostfactor Gi applied to each of the individual installments i may have adifferent value. In one embodiment, a common power boost factor isapplied to each installment.

[0087] If a negative acknowledgement or NAK corresponding to thetransmitted power boosted subpacket is received at decision diamond2014, processing continues step 2020 to determine if the power boostlimit is satisfied, i.e., has the maximum number of slots been powerboosted. If the power boost limit has not been satisfied, thenprocessing continues to step 2012 to power boost the current subpacket.When the power boost limit is satisfied at step 202, then processingcontinues to step 2010 to initiate transmission of a next successivepacket. Note that when the power boost limit is satisfied, oneembodiment begins transmission of the next successive packet on the nextslot. An alternate embodiment allows does not transmit on remainingslots, but allows the slot used for the maximum number of installmentsbefore transmitting the next successive packet. When an ACK is receivedat step 2014, processing continues to step 2010 to initiate transmissionof a next subpacket. The next subpacket is not necessarily a nextsuccessive packet. See the example of subpacket transmissionsillustrated in FIG. 8. In yet another embodiment, one or more bits inthe packet are used to indicate the intended number of installments forthe transmission of the packet. In this case, if the source receives aNAK after the transmission of the intended number of subpackets, thesource transmits the remaining subpackets, until an ACK is received, oruntil all N subpackets have been transmitted. In this case, the sourcemay transmit the additional subpackets (subpacket M+1, M+2, . . . ) atthe nominal gain, as opposed to the power boosted gain. Once thedestination decodes the packet, the destination discovers the intendedtermination target of the packet, and adjusts the power control loopaccordingly.

[0088] The ACK and NAK for each subpacket identify the correspondingsubpacket. Between transmission of the current power boosted subpacketand receipt of the NAK, the source may transmit another subpacket. Inthis case, when a NAK is received for subpacket i, the subpacket (i+1)may have been transmitted. In this way, transmission and receipt of thesubpackets may not occur in sequence. The receiver is adapted to storeeach of the subpackets until completion of all installments of a packetare completed. The receiver then reassembles the packet. Note that thesource waits a given number of time slots for the ACK or NAK. If no ACKor NAK is received, the source may assume an ACK or a NAK. Typically,the source will assume a NAK, and retransmit the subpacket or initiatehigher layer processing if the source has exceeded a maximum number ofallowable retransmissions. When a maximum number of allowableretransmissions is used without successful receipt by the destination,the source passes processing of the subpacket to higher layerprocessing, wherein the source determines appropriate action based onthe type of data.

[0089] MAC-Layer ARQ

[0090] As discussed hereinabove, in some situations, the retransmissionsare handled by a higher layer processing. The higher layer may resend ata later time and may reconfigure the data by repackaging with otherpackets. The higher layer used for this processing may depend on thearchitecture of the layering. A layering architecture 2050 for acommunication system supporting High Rate Packet Data (HRPD) consistentwith cdma2000, and as specified in IS-856, is illustrated as an examplein FIG. 15. The stack 2050 includes layers: application layer 2052;stream/session layer 2054; connection layer 2056; security layer 2058;MAC layer 2060; and physical layer 2062. Application layer 2052 providesmultiple applications, including a default signaling application fortransporting air interface protocol messages. The stream/session layer2054 provides multiplexing of distinct application stream and providesaddress management, protocol negotiation, protocol configuration andstate maintenance services. The connection layer 2056 provides air linkconnection establishment and maintenance services. The security layer2058 provides authentication and encryption services. The MAC layer 2060is the Medium Access Control Layer and defines the procedures used toreceive and to transmit over the Physical Layer. The physical layer 2062provides the channel structure, frequency, power output, modulation, andencoding specifications for the Forward and Reverse Channels. Each layermay contain one or more protocols. Protocols use signaling messages orheaders to convey information to their peer entity at the other side ofthe air-link.

[0091] The MAC layer monitors the processing of each packet. The MAClayer may be the higher layer reprocessing. A physical layer packet mayconsist of multiple MAC-layer packets, generated by differentapplications. Whenever a physical layer packet is not successfullydecoded at the destination (for example, when the packet is not decodedeven after reception of all sub-packets), then all the MAC-layer packetsembedded in the physical layer packet are lost. Some MAC-layer packetsmay be quite delay-tolerant, but at the same time, highlyerror-sensitive, requiring a loss rate much less than the target decodererror rate employed by the hybrid-ARQ and power control schemes. Datagenerated by applications, such as File Transfer Protocol (FTP), whichuse the Transmission Control Protocol (TCP) transport layer protocol areexamples of such error-sensitive packets. There is a need for amechanism to reduce the effective loss rate of error-sensitive MACpackets beyond the decoder failure rate provided by the ARQ scheme.

[0092] If a physical-layer packet fails to decode even after allsubpackets have been transmitted, the source may detect the loss of thepacket from the physical-layer NAK message received from the feedbackchannel, after the last subpacket is transmitted on the primary channel.If a lost physical-layer packet contains one or more error sensitiveMAC-packets, then these error-sensitive MAC-packets are reinserted intothe transmission queue at the MAC layer. Eventually, these MAC-layerpackets are embedded into new physical layer packets, and aretransmitted using a hybrid ARQ scheme.

[0093] In other words, the physical-layer NAK message for the lastsubpacket transmission is interpreted as an abstract MAC-layer NAKmessage, for all the error-sensitive MAC-packet embedded in thephysical-layer packet. The NAK for the last subpacket is effectively aNAK for the entire physical layer packet. At the MAC layer, this isinterpreted as a NAK for all the MAC payload contained in the physicallayer packet. Note also that the composition of the new physical-layerpacket containing these re-inserted MAC-packets may be different fromthat of the physical-layer packet that was used to send the MAC-packetsin the previous attempt. The entire packet or a part of that packet maybe reconfigured and retransmitted. Parts of the packet that containdelay sensitive information need not to be retransmitted. Note that“part of the packet” is not the same thing as a subpacket. The physicallayer packet contains data from different applications. A “part of thepacket” refers to data from one such application. The different“subpackets” of the same packet contain the same data, encoded indifferent ways. It is not necessarily the case that each subpacketcontains a small part of the physical layer packet. Data from differentapplications are not distinguished from one another at the physicallayer. Such distinction is generally made at the MAC layer or higher.

[0094] While reinserting MAC-packets into the transmission queue, thesource maintains a minimum delay or wait time prior to retransmission ofthe data in a physical layer packet. The delay allows the channel torecover from any deep fade, which is most likely the reason for failureof the earlier transmission of the packet, in spite of a fairlyelaborate and efficient hybrid ARQ scheme. The additional time diversityresulting from this deliberately induced delay increases theeffectiveness of MAC-layer retransmission, providing a highly robustmechanism for transmitting error-sensitive, delay-tolerant data.

[0095] Improving the reliability of the physical-layer ARQ messages, inparticular the ARQ message associated with the last subpacket, is a goalof system design. Here the final installment of the packet is the lastsubpacket. The Reverse Link (RL) feedback channel used to transmit thephysical-layer ACK/NAK messages is generally designed to be reliable soas to support the target decoder failure rates. However, thephysical-layer NAK after the last subpacket transmission may be used asan implicit MAC-layer NAK, which in turn is used to improve theperformance of very error-sensitive data. The MAC layer ARQ is generallyused to achieve an error rate much smaller than the error rate targetedby the physical layer ARQ. Hence, the feedback channel associated withMAC layer ARQ needs to be much more reliable than the feedback channelof the physical layer ARQ. The reliability of the physical layer ARQfeedback channel for the last subpacket may not be sufficient for thepurpose of MAC layer ARQ. Therefore, the ARQ feedback channel for thelast subpacket may have a rate target which effects a lowererror/erasure rate than the feedback channel for the other subpackets.The following discussion presents a way to enhance the reliability ofthe last NAK message, in the context of a 1xEV-DO system.

[0096] The feedback channel associated with 1xEV-DO RL is transmitted asa part of the 11xEV-DO Forward Link. The data channel, the pilot channeland the Feedback channel (also known as MAC channel) are timemultiplexed into the 1xEV-DO forward link waveform.

[0097] The structure of the Forward Link waveform is based on the notionof half slots. In one embodiment, a half-slot refers to a time durationof 0.8333 msec, which contains 1024 chips (at a rate of 1.2288 Mcps). Ineach half slot, the pilot channel is transmitted in a burst of 96 chips.The feedback channel is transmitted in two bursts of 64 chips, one oneach side of the pilot burst. The data channel is transmitted in twobursts of 800 chips, filling up the remaining space in the half-slot.

[0098] The pilot channel is used by the receiver for channel estimation.The feedback channel is decomposed into a Reverse Power Control (RPC)subchannel the ARQ channel. The RPC channel is used to carry powercontrol commands (including busy bits), while the ARQ channel is used tocarry the physical layer ACK/NAK messages from the base station(destination of reverse link packets) to the user terminals (source ofreverse link packets). The total energy available in the feedbackchannel is shared between the power control commands and physical-layerACK/NAK messages.

[0099]FIG. 16 illustrates a base station transceiver supporting oneembodiment of the present invention. The base station 3000 includes areceiver 3002 and transmitter 3006 for communication with mobilestations within a wireless communication system. The base station 3000further includes a DRC application unit 3004 for receiving a DRC datarate request from each mobile station supporting High Rate Packet. Datacommunications, a NAK/ACK processing unit 3010 for receivingacknowledgement messages from a mobile station supporting an automaticrepeat transmission technique, such as ARQ or hybrid ARQ, and a powerboost unit 3012 for applying the power boost factor to transmissions ofsubpackets. The base station 3000 further includes a packet processingunit 3014.

[0100] The base station 3000 receives data for transmission to a mobilestation, wherein the data is to be transmitted in packets. The packetprocessing unit 3014 prepares the data into packets and subpackets fortransmission. The packet processing unit 3014 performs the MAC layerprocessing. The packet processing unit 3014 generates the subpackets forprocessing, including the systematic bits and parity bits. The powerboost unit 3012 determines the number of installments for application ofthe power boosting, and generates, stores and applies the power boostfactors. In one embodiment, the power boost factors are dynamicallyadjusted, wherein the adjustment may be based on performance of a givencommunication with a given mobile station.

[0101] The NAK/ACK processing unit 3010 receives the NAK and/or ACKmessages from the mobile stations. On receipt of a negative acknowledgemessage or NAK, the NAK/ACK processing unit 3010 initiates aretransmission of the subpacket. In an automatic retransmission scheme,once the total number of allowable retransmissions expires (i.e., allretransmissions have been transmitted), any NAK received results inhigher layer processing of the subpacket, such as by the MAC layer.According to one embodiment of the present invention, when the number ofpower boost installments expires (i.e., all power boost installmentshave been transmitted), any NAK received results in termination oftransmission of that subpacket, and processing passes to a higher layer.

[0102]FIG. 17 illustrates the channel structure of the including datachannel, pilot channel, and feedback channel. The half slot isillustrated as 1024 chips. Each halfslot includes a pilot portion of 96chips and two feedback channel portions of 64 chips each.

[0103] The feedback channel is used to receive feedback informationsimultaneously with multiple user terminals, each of which beingidentified by a user index (MAC index). The feedback channel is designedto support close to 64 users, each with a unique user index between 0and 63. Associated with each user index i is a Walsh function W_(i). TheWalsh functions are binary-valued, periodic, discrete-time sequences,with the following two key properties:

[0104] 1. If n is the smallest integer such that i<2^(n), then thefundamental period of the Walsh function W_(i) is equal to 2^(n).

[0105] 2. If i and j are distinct non-negative integers, both less than2^(n) then the Walsh functions W_(i) and W_(j) are mutually orthogonalover a period of length 2 raised to the n.

[0106]FIG. 18 illustrates the ACK/NAK on the feedback channel, whereinuser i is identified by the Walsh index W_(i). The power control ACK/NAKsignal for the MAC layer is illustrated.

[0107] The following describes a method for increasing the accuracy ofthe last transmitted ACK/NAK on the feedback channel, wherein the powercontrol commands and physical-layer ACK/NAK commands are transmittedsimultaneously to multiple users. FIG. 19 illustrates applicationaccording to one embodiment. The power control command to a userterminal is a sequence of UP/DOWN commands. The UP/DOWN commands aresent to a terminal having user index i, by transmitting thecomplex-valued signal ((±1)+j 0) W_(i) over a duration of multiple halfslots (multiple of 128 chips). The ACK/NAK commands are sent to theterminal with user index i by transmitting the complex-valued signal(0±j 1) W_(i) over an integral number of half-slots.

[0108] Since i is greater than or equal to 0 and less than 64, the abovescheme ensures that the feedback channels (RPC and ARQ channels) ofdistinct users are mutually orthogonal, within each 64-chip burst of thefeedback channel. In addition, the RPC and ARQ channels of the same userare also mutually orthogonal, over the same duration.

[0109] Successive power control commands and successive ARQ commands aresent sequentially, so that successive symbols do not overlap in time. Inthe current scheme, the physical layer ACK/NAK message is transmittedover the same duration as the physical layer subpackets (4 slots).Moreover, the ACK/NAK message is transmitted at a fixed time offsetrelative to the associated sub-packet. This ensures that successiveACK/NAK messages, as well as successive power control commands, aremutually orthogonal. Alternate embodiment may provide the messages atalternate timing consistent with the needs and goals of a given system.

[0110] One embodiment improves the reliability of the physical-layerACK/NAK messages by slowing down the power control rate. In this wayeach power control command is sent over a longer duration of time, butat lower power such that the energy in each power control bit is thesame. The resulting power savings may be used to boost-up the powerallocated to the ACK/NAK messages on the ARQ channel. This approachreduces the effectiveness of power control, while improving theeffectiveness of hybrid ARQ. A well-designed system maximizes theoverall link performance through an optimal tradeoff between RPC and ARQreliability.

[0111] Another embodiment seeks to improve the reliability of the ARQchannel, without impacting power control by noting that the first fewsubpackets mostly result in physical-layer NAK messages, while the lastfew subpackets mostly result in a physical-layer ACK message. A fewsubpackets in the middle may generate a reasonable mix of both ACK/NAKmessages. Hence, we may use ON-OFF keying in response to the first fewand last few subpackets, while employing an antipodal signaling inresponse to the subpackets in the middle.

[0112] More explicitly, the physical-layer ACK and NAK messages forsubpackets in the middle (subpacket index in the range [K1, N minus K2])are transmitted with equal power relative to each other. In contrast,the NAK message of the first few subpackets (subpacket index in therange [1, K1)) may be sent with much less power than the ACK message forthe same subpackets. Note according to one embodiment, the NAK messageof the first few subpackets may be allocated zero power. Similarly, theACK message of the first few subpackets (subpacket index in the range[1, K1)) may be sent with much less power than the NAK message for thesame subpackets. Note according to one embodiment, the ACK message maybe allocated zero power. If one of the messages is sent with zero powerand the other sent with more than twice the power, relative to the powerused for ACK/NAK associated with intermediate subpackets, the system mayimprove the reliability of the first few and/or last few ARQ messageswhile using the same average power as before. Alternatively, we maysupport a larger number of ARQ channels at the same reliability, usingthe same average power as before.

[0113] Robust ACK/NAK Message

[0114] As mentioned hereinabove, the last NAK message needs to be muchmore reliable than other messages. The following technique provides away to further improve the reliability of this message. The methodprolongs the transmit duration of the ACK/NAK message, while maintainingorthogonality with the neighboring ACK/NAK messages. Given a nominaltransmit duration of an ACK/NAK message to be K half-slots, oneembodiment transmits a “robust ACK/NAK” message over a duration of up to3K. For a NAK message sent over multiple half slots, a different Walshcode or portion of a Walsh code is transmitted in each half slot. Therobust NAK message may be sent by transmitting the signal (0±j 1) W_(i)over the first K half-slots, the signal (0±j 1) W(64+i) over the next Khalf-slots, and the signal ((±1)+j 0) W(64+i) over the next Khalf-slots.

[0115] Within each half-slot, the “robust ACK/NAK” messages remainorthogonal to one another, as well as to the standard ACK/NAK messages,even though different messages may overlap in time. Note also thatwithin a half-slot, the feedback channel is transmitted within a spaceof (128 plus 96) or 224 chips (0.183 msec), an order magnitude less thanthe coherence time of most wireless channels. Therefore, orthogonalityis maintained without regard to channel variations due to fading,shadowing, etc.

[0116]FIG. 18 illustrates one application of the robust ACK/NAK message.As illustrated, a first packet is transmitted in four subpackets,wherein the first packet is labeled “PCKT 1” and the subpackets: 1.1;1.2; 1.3; and 1.4. The NAK for the subpacket 1.4 is given in twoportions, the first portion is identified as the 1^(st) MAC NAK for 1.4,and the second portion is identified as the 2^(nd) MAC NAK for 1.4. The1st MAC NAK for 1.4 is given by the code - - - - - -, and the 2nd MACNAK for 1.4 is given by the code -+-+-+. The 2^(nd) MAC NAK for 1.4 istransmitted concurrently with the 1^(st) MAC NAK for the first subpacketof the next packet, specifically subpacket 2.1 of PCKT 2.

[0117] By using this technique, it is possible to reduce the power usedon the “robust ACK/NAK” message by a factor of 3, without degradingperformance. Alternatively, the reliability of these messages may beimproved considerably (especially in fading channels), using the sameamount of power allocated to the standard ACK/NAK messages. Thistechnique may be used in conjunction to the ON-OFF signaling technique,wherein the last ACK message is sent with very little or no power,resulting in reduced average power consumption for the last ARQ message,over a large number of users.

[0118] Those of skill in the art would understand that information andsignals may be represented using any of a variety of differenttechnologies and techniques. Fore example, data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof. Reverse Rate Indicator

[0119] Presented herein is a Reverse Rate Indicator (RRI) detectionscheme and apparatus for application to a Reverse Link (RL) physicallayer, wherein the detection scheme decodes the RRI for a new incomingpacket using the knowledge of Forward Link (FL) ARQ information from agiven base station. As defined in IS-856, the RRI is transmitted on theReverse Traffic MAC Reverse Rate Indicator (RRI) Channel, which is theportion of the Reverse Traffic Channel that indicates the rate of theReverse Traffic Data Channel. For the Reverse Traffic Channel thatsupports ARQ, the encoded RRI Channel symbols are code-divisionmultiplexed with the Pilot Channel.

[0120] As illustrated in FIG. 20, a packet of data may be divided into anumber of subpackets. In the present embodiment, a packet of dataincludes 16 slots, which is then grouped into subpackets each containing4 slots. The RRI provides information as to the data rate at which thepacket is transmitted. When the subpackets are transmitted sequentiallytogether, it may be sufficient for the RRI to provide payloadinformation. Each payload is indicated by bit length, wherein thepayload bit length is associated with a known data rate. Smallerpayloads may be transmitted using fewer bits, and thus at an effectivelower data rate. Larger payloads may be transmitted using more bits, andthus at an effective higher data rate. When the packet is not receivedcorrectly, the entire packet is retransmitted. In this situation, thepayload information may be sufficient information to decode a givenpacket; however, when transmission applies incremental redundancy, thereceiver will require more information in order to decode andreconstruct the packet correctly. Incremental redundancy allows eachsubpacket to be retransmitted individually if that subpacket was notcorrectly received.

[0121] According to an incremental redundancy scheme, each subpacket istransmitted until the transmission of the subpacket is confirmed. Inother words, a subpacket is transmitted, and if a negativeacknowledgment is received, the subpacket is retransmitted. While thereis a maximum allowable number of retransmissions defined, within apacket of data, each subpacket may be retransmitted a different numberof times. The entire packet is not retransmitted, but rather eachsubpacket is treated individually. In this situation, the receiverrequires information to reconstruct the packet given each individualpacket. In other words, the receiver needs to identify individualsubpackets within a packet.

[0122] An example of incremental redundancy is illustrated in FIG. 21.Here a packet of data includes subpackets A, B, C and D. Here thesubpacket A is transmitted multiple times, each identified by an index(1), (2), etc. Note that each of the subpackets A, B, C, and D may betransmitted and retransmitted differently.

[0123] In one embodiment provided as an example, the RRI channelsupports interlaced RL data packet transmission. The RRI is used toindicate the presence or absence of data, the corresponding data rateand the instance of subgroup transmission of data packet. In otherwords, the RL supports incremental redundancy in transmissions ofsubpackets, and the RRI then indicates the data rate, as well asidentifies the specific subpacket within a packet. For a given packet,an interlace includes all of the subpacket transmissions andretransmissions for a given subpacket.

[0124] In this example, to optimize the decoding complexity versusperformance trade off, the RRI is based on the Walsh code family. Thenumber of information bits each RRI codeword carries, N_(Info), isdesigned to satisfy the following condition:

2^(N) ^(_(Info)) ≧N _(rate) ×N _(group),  (2)

[0125] wherein N_(rate) is the total number of available data rates(including the null rate) and N_(group) is the maximum number ofsubgroups that a packet may be broken into during transmission. Fordecoding performance considerations, this example uses bi-orthogonalWalsh codes, so as to slightly reduce the increase in the number ofminimum-distance neighbors to any codeword while we double the codewordspace.

[0126] In one embodiment, RRI decoding may be based on themaximum-likelihood criterion by assuming all RRI codewords aretransmitted with equal probability. The calculation then reduces to theminimum distance decoding defined by the following equation:$\begin{matrix}{( {g,i} ) = {\arg\limits_{\underset{\underset{0 \leq i^{\prime} \leq {N_{rate} - 1}}{0 \leq g^{\prime} \leq {N_{group} - 1}}}{({g^{\prime},i^{\prime}})}}\quad \min {\sum\limits_{j^{\prime} = 0}^{g^{\prime}}{{( {\overset{\sim}{R}}_{k - j^{\prime}} ) - ( R_{j^{\prime}} )_{i^{\prime}}}}^{2}}}} & (3)\end{matrix}$

[0127] wherein g indicates the index of the corresponding subgrouptransmission of the data packet; i denotes the data rate of the packet;(R_(j′))_(i′) represents the RRI codeword for the j′th subgrouptransmission of a data packet of rate i′; and ({tilde over (R)}_(k)) isthe current received RRI codeword corresponding to the current subgrouptransmission of data packet (thus ({tilde over (R)}_(k−j′)) representsthe j′th-group earlier received RRI codeword for the same interlace asthe current received RRI codeword).

[0128] While provision of the subpacket identifier or index in the RRIis sufficient information for decoding the packet, there is still greatdecoding complexity as the receiver must first decode the RRI. Thereceiver determines a number of hypotheses to try in order to decode theRRI. The number of hypotheses considers the number of available datarates, N_(rate), and the number of allowable retransmissions per packetN_(group). Each set of subpackets associated with a packet is referredto as a subframe. N_(group) subframes from the same physical-layerpacket form a frame. Note that the number of subpackets per packet mayalso be variable. With reference to Equ. (2), the total number ofhypotheses, is equal to (N_(rate)×N_(group)). In other words, thereceiver must try all of the possibilities (i.e., hypotheses) toretrieve the RRI information. This number may be quite large given theinterlaced RL ARQ structure. In addition, the minimum decoding distancesis always 1 subframe, even when there are more than 1 subpackets perpacket. This could potentially hurt the decoding performance underfading channels due to the lack of time-diversity.

[0129] In one embodiment, to reduce the RRI decoding complexity andimprove the minimum decoding distance (and hence the performance) theBase Station (BS) RRI decoder utilizes previous packet decoding resultsfor the current interlace to reduce the number of hypothesizes to betested. In particular, the BS may assume that a NAK signal to the AT isabsolutely reliable. For example, in a 4-slot RL structure as shown inFIG. 21, if the BS has not succeeded in decoding the 1^(st) subgrouptransmission of a data packet of rate i, the BS expects furthertransmissions of this subpacket. In other words, if subpacket A isreceived but decoded incorrectly, the BS expects further retransmissionsof subpacket A. On accurate decode, the BS sends an ACK to the mobilestation for this subpacket. In this situation, on receipt of the nextRRI codeword of the same interlace, ie., subpacket A, the BS may limitthe hypotheses for the 2^(nd) subgroup to those of the same data rate i.In this way, the BS is able to ignore hypotheses for different rates. Byusing such information regarding prior interlace transmissions, thedecoding complexity is greatly reduced. Specifically, the receiver isable to use historical information to make smart decisions for decodinga next received RRI. A further reduction in decoding complexity resultsfrom the observation that BS may start detection from the most recentACK'ed subpacket, as any RRI information prior to this instance does notprovide sufficient helpful information for packet decode. For example,if the AT has just sent subpacket 3 of packet A and this has beendecoded successfully, the BS will send an ACK to the AT and then startRRI hypothesis testing from the following subframe. This also allows thereceiver to reduce significant complexity in the detection process.

[0130] In one embodiment, the codeword includes a first portiondesignating the data rate information, and a second portion designatingsubpacket index information. The RRI codeword is transmitted on the RLas described hereinabove. Each data rate then has an associated RRIsymbol. The RRI symbol is then expanded to an RRI codeword fortransmission.

[0131] There is a one to one correspondence between payload size anddata rate. As

RRIWord(i, j)=(−1)^(i) W _(8└i/2┘+j) ⁶⁴

[0132] illustrated in FIG. 23, each payload has an associated payloadID. Physical Layer (PL) sub-packet (e.g., 4-slot subpacket). The RRIcodeword provides information to the receiver regarding the payloadinformation of the long packet to which the sub-packet belongs, as wellas providing the sub-packet index. FIG. 23 assigns a payload ID to eachof the different types of PL packet payload sizes. In the presentembodiment, each RRI codeword contains 6 bits of information. Four bitsencode the payload ID, and the remaining two bits encode the sub-packetindex (i.e. 0, 1, 2, or 3). The RRIs are encoded overall using 32-arybi-orthogonal codes. For the i^(th) payload ID and j^(th) subpacketindex, the RRI is encoded as:

RRIWord(i, j)=(−1)^(i) W _(8└1/2┘+j) ⁶⁴  (4)

[0133] where W_(j) ^(N) denotes the jth length-N Walsh sequence.

[0134] An RRI detection algorithm is used at the receiver, e.g., BS, todecode the RRI. As the RRI transmission parameters change from packet topacket, and this information is not provided a priori to the receiver,it is incumbent upon the receiver to determine how to decode the RRI. Asdescribed above, one method may be considered brute force, wherein thereceiver tries all possible data rates for decoding the RRI. Thedecoding is complicated further by the application of incrementalredundancy. When the RRI is transmitted as a packet composed of multiplesubpackets, each subpacket is considered in decoding the RRIinformation. Therefore, the index or identification of the subpacket issignificant in decoding the whole packet. Thus, the exhaustive set ofpossible hypotheses includes all combinations of: (i) available datarate; and (ii) each possible subpacket within the packet. In oneembodiment, 12 data rates are available and 4 slots are assigned perpacket, resulting in 48 possible combinations, including the null datarate. Note, each data rate corresponds to a payload. While it ispossible to decode each subpacket independently, doing loses theadvantage of being able to soft-combine the data across the subpacketsto provide greater time-diversity and redundancy to combat adversechannel conditions. Hence, it is desirable to detect both data as wellas RRI of a given packet by looking at all possible subpackets that havebeen sent so far. In one embodiment, an RRI detection algorithm performssequence detection, wherein the decoding is performed over a window ofRRI transmission subframes. Sequential detection multiplies the decodingcomplexity, i.e., the number of hypotheses, significantly. For a systemhaving 4 subpackets per packet with 12 available data rates, and aresultant 48 possible hypotheses, consideration of 2 subpackets willresult in (48×48) possible hypotheses. In other words, as each subpacketis considered with respect to each of the 48 hypotheses. Considerationof 4 slots results in (48×48×48×48) possible hypotheses. Therefore,design of a sequential detection algorithm seeks to: (i) minimize thenumber of possible hypotheses; and (ii) maximize the minimum decodingdistances between these hypotheses. Without optimization, sequentialdetection carried out over 16-slot detections for all possible payloadand subpacket ID combinations over a given interlace, may result in4100625 hypotheses, given a minimum-distance of 4-slots. Thus the needfor a more efficient decoding algorithm or enhancement to sequentialdetection to reduce the number of hypotheses.

[0135] Even though such RRI complications are caused naturally by thephysical-layer hybrid ARQ structure, this structure turns out to help usas well. For forward link ARQ channel detection at the mobile station,generally the false alarm rate, i.e., interpreting a NAK signal as anACK, is limited so as to be extremely low (about 0.1%). For example,this may be ensured via an erasure decoder when the subpacket ID is lessthan 3. Therefore, it is assumes that a NAK for a given subpacket, willbe correctly interpreted by the mobile station. For example, if themobile station sends a packet with payload ID 3 and subpacket ID 1, andthe BS sends a NAK for this subpacket, the BS assumes that the onlypossible transmission at the next instance will be the same packet withsubpacket ID 2. With this assumption, and several other common senserules, we can now significantly improve the RRI detection performanceand complexity. In this way, the detection algorithm determines thosehypotheses which is not possible given the history of transmissionsreceived. Typically, for a subpacket received after receipt of an ACK,the BS tries the full set of all possible hypotheses. However, for aNAK, which is more reliable than an ACK and received much often, areduced set of hypotheses is possible.

[0136]FIG. 25 illustrates an RRI transmission over time. For clarity,each subframe is illustrated with a transmission index identifying theframe. The pair (x,y) denotes the RRI word with payload ID x andsubpacket ID y. A subframe denotes the 4-slot duration of a subpacket,wherein (x[n],y[n]) denotes the received RRI word during the nthsubframe. With reference to FIG. 25, the RRI sequence detection startsat subframe n, just after the BS has sent a most recent ACK for subframe(n−3). Then, for the RRI sequence that spans subframes n, n+3, n+6 . . .n+3N, where n+3N denotes the current subpacket, the BS checks for validhypotheses with respect to RRI sequences that obey the following RRIdetection Rules.

[0137] RRI Detection Rules

[0138] Let m=n+3i for i=0,1,2, . . . N, then:

[0139] Rule 1: If y[m]=y[m−3]+1, then x[m]=x[m−3].

[0140] Rule 2: If x[m−3]=0, then y[m]=0.

[0141] Rule 3: If x[m−3]>0 and m>n, then y[m]=(y[m−3]+1) mod 4.

[0142] Rule 4: If x[m−3]>0 and m=n, then y[m]=(y[m−3]+1) mod 4 or 0.

[0143] Note that the detection process may last for a long time if themobile does not have data to send, as the BS awaits an accumulation ofinstances. To conserve system memory, one embodiment confines the traceback length (as measured in number of subframes) to at most 3 subframes,since a given packet can contain at most 4 subpackets. This leads to theassumption that a new subpacket arrives on a given interlace at subframen, wherein the most recent ACK occurs later than subframe (n−3M). ForM<4, RRI sequence detection begins at subframe (n−3(M−1)) by applyingdetection rules 1 through 4. For M=4 or higher, RRI detection beings atsubframe (n−9) by apply rules 1 through 3 only. FIG. 26 illustrates thepossible RRI detection scenarios and hypotheses given these rules. Herethe number of possible hypotheses has been effectively limited.

[0144] For implementation of such an RRI detection scheme in hardware,the design applies a systematic structure. For a given mobile station inthe previously defined embodiment having multiple available data ratesand 4 subpackets per packet, at any given instance, there may be 45possible hypotheses (states) for a received RRI word at a currentsubframe. Let (x,y) denote the state corresponding to the hypothesisthat the current received RRI word has payload ID x and subpacket ID y.For each state (x,y) at subframe n, maintain four metrics M(x,y),J[n]for i=0, 1, 2, and 3. These metrics may be generated as follows:${{M( {x,y} )}_{i}\lbrack n\rbrack} = \{ \begin{matrix}{{Corr}( {{{RRIWord}( {x,y} )},{{RxRRI}\lbrack n\rbrack}} )} & {i = 0} \\{{\max\limits_{{({x^{\prime},y^{\prime}})} \in {A{({x,y,{{ARQ}{\lbrack{n - 3}\rbrack}}})}}}\{ {{M( {x^{\prime},y^{\prime}} )}_{i - 1}\lbrack n\rbrack} \}} + {{Corr}( {{{RRIWord}( {x,y} )},{{RxRRI}\lbrack n\rbrack}} )}} & {1 \leq i \leq 3}\end{matrix} $

[0145] wherein Corr(RRIword(x,y), RxRRI[n]) denotes correlation betweenthe received RRI symbols and the RRI word corresponding to state (x,y),and A(x,y,ARQ[n−3]), a set that depends on (x,y) and ARQ[n−3] (ACK orNAK for the previous subframe) and consists of all possible collectionsof (x′,y′) for x′=0,1, . . . , 11 and y′=0,1,2,3 that satisfy thefollowing rules.

[0146] Rule 5: If y>0, then x′=x and y′=y−1;

[0147] Rule 6: If y=0 and ARQ[n−3]=NAK, then y′=3 if x′>0 and y′=0 ifx′=0.

[0148] To compare the likelihood of different hypotheses, we use a finalmetric for each state. At the given time and state, this metric dependson when the most recent ACK was sent. For RRI detection of subframe n,wherein the last ACK was sent at subframe n−3*1, if (l<4), the finalmetric for hypothesis (x,y) will be M(x,y)_(l−1)[n]. If l exceeds 4(i.e., the ACK occurs more than 4 subframes ago), the final metric forstate (x,y) will be M(x,y)₃[n].

[0149] In addition, upon sending an ACK for the current subpacket atsubframe n, the system resets the metrics for all states. For a statecorresponding to a correct hypothesis (determined by a transmitted ACK),the BS maintains current metric values. For all other states, the BSresets parameters to negative infinity (or the absolute minimum value).This assures that in operation, the RRI detection process is conditionedon historical information. In the subframe following the subpacketcorresponding to the transmitted ACK, the BS turns on an ACK switch forthis instance so that the states corresponding to subpacket ID 0 areconnected with all states from the previous subframe.

[0150] In an HRPD system, the access terminal sends an RRI signal to theaccess network indicating the payload, data rate, and subpacket index.All of this information may be used in an RRI detection scheme. Suchinformation identifies the subpacket within a packet allowing thereceiver to reconstruct the packet, as systems desire a variable packetstructure. While described embodiments consider a packet having foursubpackets, alternate systems may employ any number of subpackets perpacket while applying the concepts described herein.

[0151] From the access terminal an RRI codeword is associated with eachphysical layer subpacket. RRI codeword provides information to thereceiver regarding payload information of the long packet to which thesubpacket belongs. Additionally, the RRI codeword identifies thesubpacket identifier. In one embodiment, an RRI codeword including adata rate information portion and a subpacket index portion. The makeupof the RRI codeword is then detailed in the table, wherein eachavailable data rate is provided in kbps and is mapped to thecorresponding RRI symbol and codeword.

[0152]FIG. 22 provides a table of RL Physical Layer Packer Parameterswhich are used to map payload identifiers (ID) to each of the physicallayer payload sizes, wherein the payload sizes are given in bit length.According to one embodiments, each RRI codeword includes 6 bits ofinformation. Four bits used to encode payload ID (i.e., data rateinformation as there is a one-to-one mapping of payload to data rate)with remaining 2 to encode the subpacket index. The RRI is then encodedusing a 32-ary bi-orthogonal code. The ith payload ID and the jthsubpacket index result in an RRI encoded as: (−1)^(i)Walsh_(8└i/2┘+j)⁶⁴.

[0153]FIG. 23 illustrates data rates mapped to data channel gain,wherein the gain is given in dB. The RRI may include the data rateinformation as the payload information. For a given data rate, an RRIsymbol is applied. Additionally, each RRI symbol corresponds to an RRIcodeword. In one embodiment, the RRI symbol includes 3 bits, and the RRIcodeword includes 7 bits.

[0154] As a specific example of an embodiment of the present invention,the mobile station may employ any of 11 data rates for transmission ofthe RRI. The data rates are given as x=0,1,2, . . . , 10, wherein x=0corresponds to the null set. For a fixed ratio of payload to parity, theresulting subpacket size will vary. In this way, the RRI may be any oneof 12 different data rates. As there are 4 potential subpackets within agiven packet, there are therefore 48 possibilities of combinationsthereof. Keeping in mind the one-to-one mapping of payload size to datarate, indicates the subpacket size incurs a different number ofretransmissions.

[0155] At the receiver there is a determination made as to what portionof the packet was transmitted. By using historical transmissioninformation and eliminating those possibilities which are not valid, theBS is able to decode the RRI with less effort. FIG. 24 illustratestransmission of RRI subpackets, wherein the receiver receives thesubpackets in the order shown. A window is used to determine thespecific subpackets included in a sequential RRI detection. Asillustrated, the window begins at time t₁ and continues to time t₂. Thewindow is referred to as the sequential detection window. In otherwords, the method considers all subpackets within the window todetermine if the decode is successful.

[0156] The first endpoint of the window is set when the mobile stationtransmits a first subpacket in a packet. For decode purposes, the firstpacket is evaluated in isolation. Subsequently the second subpacket inthe sequence (still of the same packet as the first subpacket) isreceived at the receiver. The second subpacket is included in thewindow, wherein the receiver considers the first and second subpacketsin determining if the decode is accurate. According to the presentembodiment, the process continues until the window includes all of thesubpackets in a packet. Note alternate embodiments may include a smallerportion of the packet. At this point, in effect, the receiver isdecoding the entire packet together.

[0157]FIG. 25 illustrates a specific example, wherein receipt of an ACKis indicated at or before time t₃. Again, the window continues toinclude additional subpackets as they are received until a maximumnumber of subpackets is reached. The receiver is still required todetermine the parameters, e.g., data rate, for correct decoding atreceipt of each subpacket.

[0158]FIG. 26 illustrates a trellis structure 400 for eliminatinghypotheses for decoding a subpacket of the RRI transmission. The trellisillustrates each possible situation or state of the receiver, whereineach situation provides a starting point and guides the path. The firstcolumn corresponds to decisions made when a NAK has been received for agiven subpacket. An entry (a,0) corresponds to a first subpacket in thepacket, and specifically in response to the transmission of thissubpacket, the BS received a NAK. Receipt of a NAK typically means therewill be a retransmission unless the maximum number of retransmissionshas been reached. This entry is labeled (a,0). The second index refersto the number of retransmissions. The next column corresponds to a nextsequential situation or state. From the middle state there are many moreoptions for traversing a path through the trellis. Note that the trellisindicates that an ACK has been received for the corresponding state.

[0159] By traversing the trellis using the current situation, the numberof detection hypotheses may be reduced resulting in quicker processing.FIG. 27 illustrates an RRI detection method according to one embodiment.As illustrated, the method 4000 begins on receipt of a subpacket, 4002.The receiver correlates the possible RRI codewords, i.e., forms a set ofhypotheses, 4004. The receiver updates the metrics for each state. Thesequence detection window length is determined, 4008. The metricscorresponding to each state are evaluated over the sequence detectionwindow. Processing continues to select a maximum among the metrics inorder to determine which RRI symbol was transmitted, 4014. The energy ofthe RRI symbol is then compared to a threshold value, 4014. If theenergy of the RRI symbol exceeds the threshold, processing continues tostep 4016 to accept the RRI symbol decision, 4016. If the energy isbelow or at the threshold value, the RRI symbol is rejected at step4020. At step 4018 the receiver determines if the packet was decodedcorrectly. Once the packet is decoded correctly, 4018, the processcontinues to step 4022 to reset the metrics. The ACK switch is then setfor the next subpacket.

[0160] As disclosed herein, a base station or other receiver is able toreduce the decode burden incurred by implementation of an incrementalredundancy scheme and allowance of a variety of payloads, data rates,etc. The current state information, as well as historical information isused to eliminate any hypotheses that clearly can not hold for the nextRRI transmission receipt. While described herein as a method fordetecting RRI information, the present invention is applicable to othersystems wherein the receiver does not receive information specific andsufficient for correct decoding. When the receiver needs to determinethe parameters of decoding, a separate channel is used to provide thisinformation. In the present case, the RRI may be retransmitted accordingto a hybrid ARQ format. Alternate redundancy schemes may be applied tothis and other systems.

[0161] Those of skill would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

[0162] The various illustrative logical blocks, modules, and circuitsdescribed in connection with the embodiments disclosed herein may beimplemented or performed with a general purpose processor, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

[0163] The steps of a method or algorithm described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

[0164] The previous description of the disclosed embodiments is providedto enable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

What is claimed is:
 1. A method for transmission of packetized data in awireless communication system having a designated packet error rate, themethod comprising: determining a first number of installments fortransmission of a first subpacket of data; power boosting transmissionsof a second number of installments of the first subpacket of data,wherein the second number is less than the first number, wherein thesecond number is selected to satisfy the designated packet error rate;and terminating transmission of the first subpacket of data after thesecond number of installments.
 2. The method as in claim 1, wherein apower boosting gain factor is applied to each of the second number ofinstallments.
 3. The method as in claim 2, wherein the power boostinggain factor is nominally set to (N/M), wherein N is the first number ofinstallments, and M is the second number of installments.
 4. The methodas in claim 1, wherein terminating transmission of the first subpacketof data comprises: initiating a second subpacket of data after thesecond number of installments.
 5. The method as in claim 1, wherein thefirst number of installments for the first subpacket of data correspondsto a first time period, wherein terminating transmission of the firstsubpacket of data comprises: waiting for expiration of the first timeperiod; and initiating transmission of a second subpacket of data afterexpiration of the first time period.
 6. The method as in claim 1,further comprising: receiving a negative acknowledgement message aftertransmission of the second number of installments; and processing thefirst subpacket of data at a higher layer.
 7. The method as in claim 1,further comprising: receiving an acknowledgement message beforetransmission of all of the second number of installments; and initiatingtransmission of a second subpacket of data.
 8. An apparatus fortransmission of packetized data in a wireless communication systemhaving a designated packet error rate, the apparatus comprising: meansfor determining a first number of installments for transmission of afirst subpacket of data; means for power boosting transmissions of asecond number of installments of the first subpacket of data, whereinthe second number is less than the first number, wherein the secondnumber is selected to satisfy the designated packet error rate; andmeans for terminating transmission of the first subpacket of data afterthe second number of installments.
 9. The apparatus as in claim 8,wherein a power boosting gain factor is applied to each of the secondnumber of installments.
 10. The apparatus as in claim 9, wherein thepower boosting gain factor is nominally set to (N/M), wherein N is thefirst number of installments, and M is the second number ofinstallments.
 11. The apparatus as in claim 8, wherein means forterminating transmission of the first subpacket of data comprises: meansfor initiating a second subpacket of data after the second number ofinstallments.
 12. The apparatus as in claim 8, wherein the first numberof installments for the first subpacket of data corresponds to a firsttime period, wherein means for terminating transmission of the firstsubpacket of data comprises: means for waiting for expiration of thefirst time period; and means for initiating transmission of a secondsubpacket of data after expiration of the first time period.
 13. Theapparatus as in claim 8, further comprising: means for receiving anegative acknowledgement message after transmission of the second numberof installments; and means for processing the first subpacket of data ata higher layer.
 14. The apparatus as in claim 8, further comprising:means for receiving an acknowledgement message before transmission ofall of the second number of installments; and means for initiatingtransmission of a second subpacket of data.
 15. A base station apparatuscomprising: a packet processing unit adapted to receive data fortransmission and generate subpackets, each of the subpackets transmittedin a number of installments; a power boost unit adapted to apply a powerboost factor to a portion of the subpackets, an acknowledgement messageprocessing unit adapted to terminate transmission of installments for asubpacket on receipt of an acknowledgement message; and a transmitterfor transmitting power boosted subpackets, wherein the packet processingunit terminates processing of the subpacket on receipt of a negativeacknowledgement message after the portion of the subpackets istransmitted.
 16. A method for transmission from a mobile station in awireless communication system, wherein each data packet received istransmitted in a number of installments, the method comprising:transmitting a first negative acknowledgement message for a lastinstallment of a first subpacket, the first negative acknowledgementtransmitted at a first time slot; and transmitting a second negativeacknowledgement message for the last installment of the first subpacket,the second negative acknowledgement transmitted at a second time slot,wherein the second time slot is designated for the first subpacket ofthe next packet.
 17. The method as in claim 16, wherein the firstnegative acknowledgement has a first bit pattern, and the secondnegative acknowledgement is a different bit pattern orthogonal to thefirst bit pattern.
 18. An apparatus for transmission from a mobilestation in a wireless communication system, wherein each data packetreceived is transmitted in a number of installments, the apparatuscomprising: means for transmitting a first negative acknowledgementmessage for a last installment of a first subpacket, the first negativeacknowledgement transmitted at a first time slot; and means fortransmitting a second negative acknowledgement message for the lastinstallment of the first subpacket, the second negative acknowledgementtransmitted at a second time slot, wherein the second time slot isdesignated for the first subpacket of the next packet.